This invention relates to ultrasonic nondestructive testing and, more particularly, to a test method which is able to identify defects and determine orientation and size via a pulse analysis method.
Current nondestructive testing methods for metal weld and high pressure containment vessel defects fail to provide sufficient information upon which satisfactory fracture mechanics lifetime--prediction models can be predicated. This is due to the demand for more valid and reliable defect characteristics information occasioned by nuclear generating plants and the severe physical constraints encountered in attempting to provide such information. Useful quantitative information about the characteristics of the defect may be obtained by peak-amplitude, arrival-time, or frequency-content analysis.
Because small defects in areas of high mechanical or thermal stress may affect the service strength of the parts sufficiently to warrant rejection, and because measurement of the peak amplitude of the principal defect echo is unreliable for small defects, a new nondestructive testing technique is required.
An additional problem encountered by many conventional ultrasonic tests is the need for extensive calibration of the apparatus for the testing of any part. It is also difficult to repeat these tests to determine in-service progression of the defects so it can be determined whether the defect is "malignant" (propagating) or "benign" (non-propagating).
Included as representative of the state-of-the-art, "Problems Associated With Ultrasonic Reference Defects", R. Frielinghaus, J. Krauthramer and U. Schlengermann, Non-Destruction Testing, April 1970, pages 125-27; "Sizing Crack-Like Defects by Ultrasonic Means", M. G. Silk, Research Techniques In Nondestructive Testing, 1977, Volume III, pages 51-99; and U.S. Pat. No. 4,137,779, "Methods and Arrangement for the Determination of Crack-Depths in Ultrasonic Nondestructive Testing" by H. Wustenberg and E. Schulz, filed Dec. 7, 1973. Additionally, a paper entitled "Defect Identification And Sizing By The Ultrasonic Satellite-Pulse Technique" which was delivered to the Advanced Research Project Agency/Air Force Review of Progress in Quantitative NDE during July 8-13, 1979 by the inventor is included.
Frielinghaus discusses the fact that ultrasonic characterization of reference defects is complicated by the existence of scattered waves. While some attempt is made therein to discuss the composition of an echo from a sawtooth groove, no attempt is made at deriving information concerning the defect itself.
Silk completely ignores inclusion-like defect characterization as is described in the current invention. It further does not deal with directly diffracted or scattered satellite pulses produced and recorded by a single probe. The publication, in fact, teaches away from the present invention stating that "The single probe approach seems to be less accurate than the transmission approach, because of the weak reflection from the crack tip in many cases and the presence of other interferring pulses arising from defect irregularities; mode conversion, etc." Id. at 83. The present invention surmounts those difficulties. The Silk publication further does not disclose any means of self-calibration or direct-readout capability.
Wustenberg teaches directly away from the present invention in that it utilizes the defect as a sound beam stop rather than as an echo pulse producer. Wustenberg "ascertain[s] the depth propagation of the defect by a marked increase in intensity of the received signal when the intersection of the respective lines along which the ultrasonic wave is transmitted and the scatter signal is received reach beyond the innermost limits of the defect." Id. at page 4, lines 54-58. The Wustenberg method thus requires two separated probes to find a point immediately below the defect. The use of the term "scatter signal" as used therein identifies waves diffracted at structural inhomgeneities as opposed to circumferential scattering due to defect surface wave radiation.